U.S. Pat. No. 4,093,709 describes biodegradable (or "bioerodible") ortho ester polymers. The polymers are the reaction products of an orthoester or orthocarbonate with a polyol. The reaction is carried out at elevated temperature, under reduced pressures and requires a relatively long reaction time. A drug or other beneficial agent is entrapped (dispersed) in the polymer and is released therefrom by diffusion or a combination of diffusion and polymer degradation.
U.S. Pat. No. 4,304,767 describes poly(orthoester) polymers that are made by reacting a ketene acetal having a functionality of two or more with hydroxyl containing compounds having a functionality of two or more.